1. Field of the Invention
The present invention relates to a semiconductor light emitting element such as a monolithic type LED (light emitting diode) which is equipped with a light emitting region formed on a GaAs substrate where an p-n junction surface is made of material such as GaAlAs. The present invention more particularly relates to the semiconductor light emitting element suitable for use as an infrared light source for an automatic focusing mechanism assembled in a camera and where light leakage from an end of the light emitting region is minimized, an interval between the light emitting elements is relatively narrow, and a reliable distance-measuring capability is achieved.
2. Description of the Prior Art
With reference to FIG. 1, there is shown a cross sectional view of the conventional semiconductor light emitting element. In the same figure, the semiconductor light emitting element is a monolithic type GaAlAs As infrared LED and is equipped with three-point light emitting elements.
With still reference to FIG. 1, the conventional semiconductor light emitting element presents the following structure, wherein conductive regions 108 are formed on a p type GaAs substrate 106. The element includes a double heterojunction (DH) structure such that a GaAlAs As current restriction layer formed with the conductive region 108 is formed on the substrate 106. The double heterojunction type GaAlAs As layer includes an n-type Ga.sub.l-x Al.sub.x As current restriction layer 105, a p-type Ga.sub.l-w Al.sub.w As cladding layer 104, a p-type Ga.sub.l-z Al.sub.z As active layer 103, and an n-type Ga.sub.l-y Al.sub.y As cladding layer 102 which are formed in sequence. Then, an ohmic electrode 101 is formed on the cladding layer 102 and is opened so that the light can be emitted externally from the conductive region 108. Thereafter, the light emitting elements adjacent to each other are electrically isolated by performing a halfway dicing on a region between adjacent light emitting elements so as to cut through a p-n Junction. As a result thereof, respective light emitting elements are independently operative. Here, the halfway dicing means a dicing which does not perform a full-cut dicing.
When the semiconductor light emitting element thus constructed above is, for example, adopted for a light source of infrared rays for a camera's automatic focusing mechanism, the infrared rays emitted therefrom are passed through a collimator lens into a parallel beam toward a subject. Thus, the light reflected from the subject is sensed by a light receiving element, and a distance to the subject is measured in accordance with a trigonometrical survey method.
In the above-mentioned conventional example, there is used the halfway dicing technique as an electrically isolating means. Therefore, when a light emitting element is, for example, rendered conductive, a light h' guided by the p-type Ga.sub.l-z Al.sub.z As active layer 103 is irradiated externally from dicing grooves, together with a light h from the conductive region 108 (see FIG. 1). Then, consulting a near field pattern which indicates a light density of light emitted from the semiconductor light emitting element, the light h' irradiated from the p-type Ga.sub.l-z Al.sub.z As active layer 103 shows a significant level of density against the light h emitted from the surface of the conductive region 108. It is to be noted here that the light h' is an unwanted light which may be a major cause for inaccurate distance measuring.
For example, when used as the light source for the automatic focusing mechanism, the light h' irradiated from the grooves, that is, the light h' which is leaked laterally from the p-type Ga.sub.l-z Al.sub.z As active layer 103, may be detected by the light receiving element so as to indicate an improper distance between the camera and the subject, so that there is caused an out-of-focus problem or the like. In order to alleviate such a problem with reference to FIG. 1, there is provided a sufficient interval d between the conductive regions 108 and the end faces of active layer 103 at the groove sidewalls, so that the unwanted light can be damped and the lateral unwanted light can be suppressed.
With reference to FIG. 6, there is shown a relationship between the distance d and the relative light density (h' ) at the end of LED element relative to that of conductive region (h). For example, in order to suppress the relative density to 3% or therebelow, the interval d needs to be more than 80 .mu.m. However, there is a limit in reducing the distance d between the light emitting elements and there lies a great difficulty in achieving a semiconductor light emitting element where the interval d is minimal and a distance measuring performance is optimal at the same time.
The halfway dicing accounts for the cause for light leakage. In other words, with reference to FIG. 5 which is an enlarged view of a portion circled by doted lines in FIG. 1, a shape realized by the dicing is an acute-angled surface. That is, an opening interval d1 in the surface of the light emitting element is greater than an interval d2 of the light emitting region in the vicinity of the p-type Ga.sub.l-z Al.sub.x As active layer 103. For instance, when depth of the halfway dicing is 60 .mu.m, opening interval d1 would be 35 .mu.m and the interval d2 be 32 .mu.m. Thereby, a portion of light irradiated from the end of the light emitting active layer 103 is detected at an upper portion of the semiconductor light emitting element.
As mentioned above, since there is commonly used the halfway dicing and the shape of element isolating portion is of the acute angled type in the conventional semiconductor light emitting element, the light is leaked in the lateral directions from the isolating portion. In order to alleviate such the problem, there is provided an increased interval between the light emitting elements, so that the light is damped and the laterally leaked light is suppressed. However, the conventional technique set a limit in further dense integration therefor. Moreover, when, for example, used for the light source for the camera's automatic focusing mechanism, there lies great difficulty in realizing a semiconductor light emitting element in which the interval therebetween is minimal and a distance-measuring accuracy is maximal.